Optic signals are widely used to communicate information from one point to another. One well-known technique is fiber optic communication, as used for telephone and data communications. An internally reflecting light pipe, such as a fiber optic cable, is used in conjunction with a light source and a light detector to transmit data. A light signal is pulsed in a pre-determined pattern, representative of the information, and imposed upon one end of the fiber optic cable. Because the cable is internally reflecting, the signal reflects back and forth in the interior of the cable, with little or no loss to the outside. These cables have specifically designed indices of refraction, and extremely high transmittancy, so that little signal loss is experienced. At the other end of the cable is an optical detector that receives the pulsed signal.
Optical waveguides are another way to transmit optical signals. A waveguide is similar to a fiber optic cable, but generally the light is transmitted down an empty cavity rather than through a glass or plastic fiber. The waveguide generally is coated with a highly reflective coating that causes the signal to be totally reflected from one side of the guide to the other. Waveguides are used for communicating signals at all frequencies of the electromagnetic spectrum, for example at radio frequencies and radar frequencies, in addition to optical frequencies.
The problem with all the prior art optical communications media is that they are fixed in the transmission mode. That is, in order to pass information, the light beam must be pulsed on and off. The fixed internally reflecting mechanism prevents the waveguide from being intersected to another waveguide, because then the signals would get intermixed at the intersection. It would be a significant addition to the art if waveguides could be coupled together without having the problem of cross-talk.